1. Field of the Invention
The present invention relates to a resin-molded electronic component having lead terminals, and more particularly, to a chip type solid electrolyte capacitor having solder plated lead terminals, and a process for manufacturing the same.
2. Description of the Related Art
As the weight and size of electronic equipment is progressively reduced, and as surface mounting technology has advanced, the chip type component such as a solid electrolyte capacitor featuring a small size and high capacity has enjoyed an increasingly expanded market scale and is used in various applications.
Conventionally, as shown in FIG. 8, a chip type solid electrolyte capacitor has a capacitor element 1 having a cathode layer 3, an anode lead 2, an anode lead terminal 8 connected to the anode lead 2 by welding or the like, and a cathode lead terminal 9 connected to the cathode layer 3.
Moreover, the cathode layer 3 and the cathode lead terminal 9 are connected by a conductive adhesive 10 such as silver paste. The capacitor is packaged by resin 6, leaving portions of the anode and cathode lead terminals 8 and 9 exposed. In addition, the anode and cathode lead terminals 8 and 9 are bent along the outer surface of the resin package 6. Since these lead terminals 8 and 9 are pre-plated with a plating layer of solder or the like by a direct current plating method using a linear current waveform as shown in FIG. 9, it has the following disadvantages (1) and (2).
(1) Organic components contained in a plating solution such as a brightener or dispersant are incorporated into the plating layer. As a result, the plating layer of solder or the like formed on the anode and cathode lead terminals 8 and 9 contains a considerable amount of the following organic substances.
Sample: Plating film formed by direct current plating Detected components:
Dichlorotoluene, PA1 N,N,2,6-tetramethylbenzeneamine, PA1 trichlorobenzene, PA1 chlorobenzenemethanol, PA1 dichlorobenzaldehyde, PA1 dichlorobenzenemethanol, PA1 lauric acid methyl
When such pre-plated lead terminals are employed in a resin-molded type electronic component, the organic substances in the plating layer of solder or the like are vaporized by thermal stress when mounting the component to generate a considerable amount of gas.
The gas thus generated in an adhering interface between the conductive adhesive 10 and the cathode lead terminal 9 affects connection reliability, and reduces the connection strength between the conductive adhesive 10 and the cathode lead terminal 9. In a worst case, the cathode lead terminal may peel off to result in an electrically open circuit.
(2) The plated solder on the lead terminals 8 and 9 in the resin package 6 tends to elute from the resin package to form a solder ball 7. This occurs when an excessive amount of an organic substance is generated due to thermal stress in mounting the electronic component. The resulting solder ball 7 can short circuit conductive patterns when the component is mounted on a printed circuit board.
To avoid the foregoing disadvantages, it is possible to plate only the exposed portion of the lead terminals. But such selective plating increases production cost.